T-mobile has a full range of sim only deals. Below there is t-mobile deals galore. As you can see the deals are all fairly similar network by network so it just really depends which network is best suited to your needs.

£15 per month - 350 mins & unimited texts - More info

£20 per month - 600 mins & unlimited texts - More info

£25 per month - 800 mins & unlimited texts - More info

£30 per month - 1400 mins & unlimited texts - More info

£35 per month - 1800 mins & unlimited texts - More info

As well as offering a higher range of sim only deals T mobile also offers unlimited internet on all of its deals apart from the £15 a month deal. If you are on a budget I suggest you stick to Vodafone, O2 or Virgin as they all offer cheaper starting packages.